The first episode of the series, which stars Richard Fleeshman and Sarah Lancashire, averaged 4.64m (20%) for BBC One, putting the channel in first place during the 9pm hour.
CSI pulled in 3.01m (13%) for Five, a drop of 360k on last week's episode.
The final instalment of ITV1's Holloway - a focus on life at the London women's prison - drew 3.74m (16.1%), while BBC Two's Horizon managed 2.06m (8.9%).
The Sex Education Show vs Pornography - the second in Channel 4's four part series - logged 2.28m (9.9%), an increase of 200k on last night's show.
Holby City was in the lead at 8pm, drawing 5.95m (26.8%) for BBC One during the hour. Its nearest competitor, ITV1's new series Cops With Cameras, attracted 3.62m (16.3%).
BBC Two's Coast was seen by 2.19m (9.8%) while 2.01m (9.1%) tuned in for the final episode of Supersize vs Superskinny on Channel 4.
Five was last for the hour, drawing 1.01m (4.6%) for Hitler's Secret Bunkers: Revealed.
Overall, BBC One came out on top in primetime with an average share of 23.4% to ITV1's 18.7%. Channel 4 was third with 8.6% (+1: 0.9%), followed by BBC Two with 7.9% and Five with 7.4%.
Elsewhere, Shameless drew 776k (9.7%) for E4 at 11pm, and 669k (3.3%) tuned in for Agatha Christie's Marple on ITV3 at 8pm.
The latest episode of BBC Three comedy Horne & Corden took 650k (4.5%) between 10.30pm and 11pm.